A number of processes for the production of bituminous binders of the aforementioned type are known. When ordinary bitumen is combined with a thermoplast or thermoplastic material an improvement in the properties of the binder is accomplished. Such modification of the bitumen often requires a relatively great expenditure of time, energy and labor because a number of different thermoplastic materials, whose addition to bitumen is capable of improving its properties considerably, are not readily soluble in bitumen. Accordingly, it is difficult to achieve uniform dispersion or homogenization of these materials. Although there do exist thermoplastic materials suitable for the modification of bitumens which have better solution properties in bitumens, these thermoplastic materials are often expensive. Moreover, construction materials produced with binders that contain such soluble thermoplastic materials often have lower physical strength than those construction materials whose binder is a bitumen treated with relatively non-soluble thermoplasts.
Known processes for combining bitumen and types of thermoplastic materials which are not readily soluble in bitumen involve heating a mixture of bitumen and thermoplastic material to a high temperature, typically at least 240.degree. C. and in some instances over 310.degree. C. This causes the molecules of thermoplastic material to disintegrate into fragments which, upon stirring, are dispersed in the bitumen. In some processes, such a treatment is carried out over a period of several hours, or even days. Such processes which involve high temperatures, while providing greater solubility or dispersion, have the shortcoming that the bitumen itself undergoes some disintegration. In many instances it is difficult to predict the sensitivity of a bituminous material to heat, batch to batch variations being very common.
Most known methods of preparing bituminous/thermoplastic composition attempt to mix a heated bituminous/thermoplastic mixture only enough to ensure thorough mixing. All such processes, however, have the disadvantage that the total mechanical energy used for mixing has been difficult to determine correctly, resulting in products having inferior mechanical properties. For example, in those cases in which too little stirring or energy feed has been used, products having poor physical properties are produced and in those case in which too high an energy feed has been employed, an unnecessary expenditure of energy or excessively severe disintegration, especially of the bitumen results. A process is described in U.S. Pat. No. 4,314,921 which process allows the treatment time to be shortened by using forceful mixing under high shearing force. However, this process requires the mixture to be subjected to a temperature of between about 260.degree. C. to 310.degree. C.
The prior art methods for mixing utilize an intensively driven force, whereby a mixture, such as a mixture of bitumen and polyethylene, are subjected to a combined thermal and mechanical load. Upon completion of this mixing there is found a weakening of the spectral lines of the X-ray spectrum which relate to the characteristics of the crystal structure of the synthetic material constituent, assuming, of course, the treatment has been continued long enough at the disintegration temperature of the constituent or constituents.